If you think it likely your question will be RAFOed, then ask an open ended question. Say something like:
- "What can you tell us about X?"
- "There's been a lot of discussion about how X, and Y and Z work together. What can you add?"
- "Can you give me a tiny hint about X?"
- "I've been talking with people about X, and they have different opinions. What line of enquiry should we be pursuing here?"
- "Previously you said X about Y. Could you expand/clarify that?"
- "In an interview once, RJ talked about X and Y. I'm not quite sure I understood what he was saying... did he mean Z?"

These questions get him looking in his mind for things he can tell you rather than things he can't. They are open ended, so he is free to supply more information than you asked for. If he would have RAFOed the direct question, he will now instead tell you things around the area of the topic that might well be helpful.

Do not mention RAFO in the question. If you do, you put the concept to the front of his mind. The first thing he thinks when he hears your question will no longer be "what is the answer?", it will be "can I think of even one semi-plausible reason to RAFO it?".

You should be discouraging him to RAFO by keeping the concept out of his mind. Do not mention RAFO in the question. In fact, if he RAFOs something then change topic to something completely different in order to get it out of his mind, and come back to the RAFOed area later with a slightly different open-ended question. Otherwise you will get an RAFO-flow-on effect where he has 'RAFO' at the front of his mind and will keep saying it.

A practical example...
Fail: "Who killed Asmodean?"
Better: "People have tried to determine who killed Asmodean many different ways. Some fans made a complete list of suspects and tried to eliminate each one with alibis. Others fans have looked for motive, others fans have thought about opportunity, others fans talked about what weapon might have been used to kill him, other fans have speculated on whether other channelers in the palace might have felt the killer channeling etc. Don't tell me who killed him. But could you please give a small hint about what lines of enquiry might be worth further discussion?"

The first way of asking is idiotic - a 100% guaranteed RAFO. But the second has the very real possibility of getting a meaningful response. A couple of Q&A reports have, for example, noted that BS seemed to imply at times that Balefire was the means of Asmodean's death. That could be worth an outright question, eg "In some of the past signings you seemed to imply that Balefire was the cause of Asmodean's death. Was that a misunderstanding of what you said, or were you speculating, or can you confirm that?"

Questions about previous answers are super-good because they can't really be RAFOed. If he's already answered something, the very least he's going to do is answer it again, and at most he will add huge amounts more information. Even if he tries to say the same thing again he'll use slightly different words the second time which reveal information.

The real winner is where you tell him RJ said something... because then (regardless of whether it is true that RJ said it) he will believe it's okay to talk about that subject because RJ already has! So all you black ajah liars get out there and say things like "In one of the interviews RJ explained how the One Power comes from the Creator, but I'm not sure I understood his explanation, could you clarify?" A good way to do it is to take a faction view-point and assert as part of your question that RJ answered that affirmatively, and watch for BS's reaction. See if BS responds with "well that's certainly not true, so RJ wouldn't have said that", or a "Yes, and also...".